Field of the Invention
The invention relates to an exhaust gas aftertreatment component with an HC adsorber function. The invention further relates to an exhaust gas system having such an exhaust gas purification system and to a vehicle which has such an exhaust gas system.
The use of catalytic converters in the exhaust gas systems of internal combustion engines is nowadays common practice. For example, in particular in the case of diesel engines, oxidation catalytic converters are used, which convert unburnt hydrocarbons (HC) as well as carbon monoxide (CO), and, in the case of diesel engines and Otto cycle engines, reduction catalytic converters are used, which convert nitrogen oxides (NOX). Furthermore, three-way catalytic converters are known that combine the function of oxidation catalytic converters and reduction catalytic converters, and thus catalytically convert all three components and are mainly used in Otto cycle engine. In principle, all catalytic converters require a specific minimum temperature in order to provide a sufficient conversion performance. As a criterion for this, the so-called light-off temperature or start-up temperature is used, at which the catalytic converter converts 50% of the limited exhaust gas components. After a cold start of the engine, this temperature has usually not yet been reached, so that, unless further measures are taken, the emissions, which are referred to as start emissions, leave the exhaust gas system unconverted.
The desire for a further reduction of emissions as well as the progressive lowering of exhaust gas limit values also require the reduction of the start emissions and thus require that the operating temperatures of the catalytic converter system are reached sooner. Current and even more so future exhaust gas emission control legislation therefore requires that also the start emissions are measured for determining the total emissions of a vehicle in standardized driving cycles.
A common measure for reducing the start emissions is to dispose relatively small volume precatalytic converters, which are also referred to as primary catalytic converters, close to the engine,
Due to their small volume and their placement close to the engine, precatalytic converters reach their light-off temperature relatively quickly and then take over the conversion of a large part of the emissions until a main catalytic converter, which is provided downstream, also reaches its operating temperature.
From German Patent Application No. DE 102 01 042 A1 an exhaust gas catalytic converter having a monolithic ceramic carrier body is known, which has an inner region and an outer region, wherein the inner region has a higher cell density than the outer region. The flow channels of the inner and outer regions that pass axially through the carrier body have a catalytic coating (washcoat). Due to the higher cell density of the inner region, this region has a higher catalytic converter activity than the outer region. A swirl generator is disposed upstream of the catalytic converter carrier, wherein the swirl generator, at low flow velocities of the exhaust gas, that is, in case of low engine load ranges, directs the exhaust gas flow essentially into the inner region and, at higher flow velocities, that is in case of higher loads, into the outer region. This arrangement achieves that, after a cold start, initially the exhaust gas flow in the inner region is catalytically treated, wherein, due to the exothermic heat release, the inner region is heated relatively quickly and thus also hears the surrounding outer region.
U.S. Patent Application Publication No. 2002/0132726 A1 describes an exhaust gas system which includes a main catalytic converter and, downstream therefrom, Iwo parallel exhaust gas lines which can be selectively closed or, respectively, opened through the use of a switchover valve. The two parallel exhaust gas lines have a concentric configuration with an inner main line surrounded concentrically by a side line in which a ring-shaped HC adsorber is disposed. A return line branches off from the side line upstream from the HG adsorber, wherein the return line which feeds hydrocarbons, which are unburnt and desorbed from the adsorber, to the internal combustion engine. After a cold start the inner main line is closed and the exhaust gas flow is guided over the HG adsorber, which adsorbs and/or chemisorbs the unburnt hydrocarbons HG and hydrocarbons not converted by the not yet operational main catalytic converter. Once the main catalytic converter has reached its operating temperature, and thus ensures a sufficient HC conversion, the exhaust gas flow is directed into the main line. Due to the heating now taking place, the hydrocarbons desorb from the HG adsorber and are delivered to the engine combustion via the return line.
Furthermore, a similar concept is known that also uses the concentric structure of an HC adsorber provided outside and a main line provided inside, wherein in this concept the main catalytic converter is however not connected upstream but downstream from the HC adsorber. In this configuration, the return line described in U.S. Patent Application Publication No, 2002/0132726 A1 is omitted. Instead, the desorbed hydrocarbons are converted by the main catalytic converter connected downstream.
For the HC adsorber concepts discussed above, it would be desirable to equip them with an additional particulate filter function. Filter functions can however only be achieved through the use of ceramic carrier bodies (monoliths). However, if such monoliths are provided with a central bore, in order to realize the bypass function which bypasses the HC adsorber, the mechanical stability of the carrier body and thus its service life decreases. For this reason and also because of the difficulty of producing ring-shaped ceramic carrier bodies, metal carrier bodies are used in the conventional concepts. Just like ceramic monoliths, metal carrier bodies too have a plurality of longitudinally extending flow channels, which are, however, produced by the combination of a corrugated sheet metal and a flat sheet metal, which are wound in the form of a spiral. A particulate filter function, which is based on partly closed flow channels, is not possible with metal carrier bodies.